Varying Pulse Frequency Research Articles

Characteristics of high-power impulse magnetron sputtering (HiPIMS) deposited nanocomposite-TiAlSiN coating under variable pulse frequencies

In the present study, nanocomposite-TiAlSiN coatings were deposited on WC-Co blocks using HiPIMS technology by varying pulse frequency. Its immediate effect on V–I signature and subsequent results on coating characteristics was critically investigated. Both substrate and target were negatively biased in pulsed mode but the voltage pulses on substrate was set with an offset of 40 μs, with respect to those on targets to avoid gas ion entrapment within coating. Variation of elemental composition, cross-sectional morphology, surface topography, hardness, and adhesion strength of the coating deposited under different pulsed frequencies, were analyzed in depth. TiAlSiN at the highest frequency, showed significant improvements in hardness and scratch resistance. A significant rise in Lc3 was recorded to be from 137.5 to 158.5 N when the pulse frequency was increased from 1 to 4 kHz. On the other hand, the peak target current was found to decrease from 340 A to 106 A. XRD spectra of TiAlSiN showed a peak shift from AlN (200) to TiAlN (200). Higher deposition rates were achieved with higher frequency but a compromise on surface smoothness, which was measured (Sa) with an increase from 9.42 to 14.32 nm.

Preparation and Investigation of Ni–Co–P Alloy Coatings Using Jet Electrodeposition with Varying Pulse Parameters

Ni–Co–P alloy coatings were successfully fabricated by jet electrodeposition with varying pulse frequencies and duty cycles in order to prolong the longevity of steel C1045 substrates. The results showed that the microstructures and properties of samples were significantly affected by pulse frequencies and duty cycles. All the samples with varying pulse frequencies and duty cycles exhibited a face-centered cubic (FCC) structure. Additionally, the average grain size of the samples reached 20.6 nm. The microhardness of the coatings was observed to first increase, and then decrease, with a rise in pulse frequencies and duty cycles. The microhardness reached 656.2 HV0.1, and the wear scar width of the coatings reached 414.4 µm at 4 kHz pulse frequency and 80% duty cycle. Additionally, the corrosion current densities (Icorr) of samples reached a minimum value of 0.74 µA·cm−2, the corrosion rates (Rcorr) reached a minimum value of 8.9 µm·year−1, and the charge transfer resistance (Rct) reached a maximum value of 8.36 × 104 Ω·cm−2, which indicated the optimal seawater corrosion resistance of the deposited coatings.

Pulsed Mechanical Surface Treatment—An Approach to Combine the Advantages of Shot Peening, Deep Rolling, and Machine Hammer Peening

Several manufacturing processes are used to beneficially influence the surface and subsurface properties of manufactured parts. Different aspects such as the surface topography or resulting residual stresses are addressed using different manufacturing processes. This paper presents the first approach for pulsed mechanical surface treatment (PMST), a new manufacturing process aiming to combine the mechanics used in deep rolling and shot or hammer peening. The process can generate a defined surface topography while constantly impinging a mechanical impact on the workpiece. Two different tools (type 1 and type 2) have been designed to approach this new concept. Hardened carbide pins are used for type 1 to prove the concept using a simpler kinematic and resulting in a burnishing-like process. For type 2, hardened roller is used and results in an actual rolling process. Specimens made of S235 are processed in experiments with tool type 1 with varying pulse frequency and feeds. The resulting surface topography is described using optical measurement systems while micro-hardness measurements are used to describe the subsurface properties. The results in general show an increase of hardness in the surface and subsurface layer while the resulting surface topography can be directly controlled by the process parameters and therefore be designed for specific functional properties.

Higher frequency electrical stimulation enhanced myloglossus satellite cell differentiation by upregulating expression of Pax7 mRNA, MyoD, myogenin and MyHC protein.

We investigated the effect of electrical stimulation (ES) of varying pulse frequency on differentiation and proliferation of canine myloglossus satellite cells in vitro. Cellular viability and proliferation were assayed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) assay and flow cytometry fluorescence-activated cell sorting analysis. Cellular differentiation and expression of mark molecule were assayed by Real Time-PCR and Western blot. With increasing frequency ES, we found a significant increase in Myod (r=0.988, p<0.0001), myogenin (r=0.988, p<0.0001), MyHC-slow (r=0.988, p<0.0001), MyHC-fast (r=0.875, p<0.0001) protein expression, and Pax7 mRNA expression (r=0.712, p=0.001). Pax7 mRNA expression and MyoD, myogenin, and MyHC protein expression were increased with increment of electrical stimulation frequency in myloglossus muscle satellite. Higher frequency ES enhanced myloglossus satellite cell differentiation, not proliferation and viability.

Effect of Electrodeposition Current and Pulse Parameter on Surface Mechanical and Electrochemical Behavior of Ni–W Alloy Coatings

Ni–W alloy coatings have various applications because they are capable of replacing hard chromium coatings due to their corrosion, oxidation, wear, and hardness properties. Moreover, these alloys demonstrate excellent mechanical and thermal stability at high temperatures leading to possible specialized applications of such coatings. In this study, the effect of pulse frequency and current density on the structure and properties of electrodeposited Ni–W coating were investigated. Pulse electro-co-deposition technique was employed to synthesize Ni–W alloy coatings by varying pulse frequency and current density. The deposition process was performed in the newly established deposition bath that does not contain surfactants and stress-relieving agents. The Ni–W-coated samples were evaluated to determine surface mechanical (microhardness and wear) and electrochemical properties. Phase formation, microstructure, and compositional analysis of Ni–W alloy coatings were examined by XRD, SEM, and EDS, respectively. Microstructure examination revealed that morphology of the coating varied with pulsed frequency and current density. An increase in the current density at fixed pulse frequency improved the surface mechanical properties (hardness and wear properties) owing to higher W content, fine, and dense structure of the coating. The maximum hardness (920 HV) and wear resistance were observed in the Ni–W coating that was obtained at the current density of 60 mA cm−2 and frequency of 2 kHz. Electrochemical polarization test and EIS study carried out in 3.5 wt pct NaCl solution reveal that a decrease in corrosion resistance of the coating is due to finer morphology or strained matrix whereas higher W content improves the corrosion resistance.

Discrete-Phase Modelling of an Asymmetric Stenosis Artery Under Different Womersley Numbers

Understanding the hemodynamics in the post-stenotic region of an asymmetric stenosis is of paramount importance in the study of atherosclerosis progression. Numerically, the analysis becomes more complex when a discrete phase is added to the continuous phase in order to understand the behaviour of atherogenic particles in a pulsatile flow environment. In the present study, discrete-phase modelling (DPM) of an asymmetric and symmetric stenosed artery models has been carried out at different Womersley numbers. The objective is to understand the correlation between the discrete-phase (atherogenic) particle behaviour with the characteristics of continuous phase (blood) under varying pulse frequencies. Continuous phase is modelled by time-averaged Navier–Stokes equations and solved by means of pressure implicit splitting of operators algorithm. DPM has been carried out with one-way coupling. The transport equations are solved in the Eulerian frame of reference, and the discrete phase is simulated in Lagrangian frame of reference. The study brings out the importance of helicity in the atherosclerosis progression. Result shows that the asymmetric stenosis model exhibits less helical flow structure and the vortical structures are not getting transported to the downstream. Consequently, the average particle residence time (PRT) of the atherogenic particles is one order higher than the symmetric stenosis model. Low PRT leads to enhanced mass transport in the arterial flow and triggers further occlusion/plaque build-up at the post-stenotic region. The extent of asymmetry in a diseased artery may be considered as a useful parameter in understanding the rate of progression of atherosclerosis.

Crystal Structure, Microstructure and Mechanical Properties of NbN Coatings Deposited by Asymmetric Bipolar Pulsed DC Sputtering

Single phase niobium nitride (NbN) coatings were deposited using asymmetric bipolar pulsed dc sputtering by varying pulse frequency and duty cycle of pulsed plasmas. Crystal structure, microstructure, morphology and mechanical properties were examined using XRD, FE-SEM, AFM and nanoindentation. Upon increasing pulse frequencies and decreasing duty cycles, the coating morphology was changed from a pyramidal-shaped columnar structure to a round-shaped dense structure with finer grains. Asymmetric bipolar pulsed dc sputtered NbN coatings deposited at pulse frequency of 25 ㎑ is characterized by higher hardness up to 17.4 ㎬, elastic modulus up to 193.9 ㎬, residual compressive stress and a smaller grain size down to 27.5 ㎚ compared with dc sputtered NbN coatings at pulse frequency of 0 ㎑. The results suggest that the asymmetric bipolar pulsed dc sputtering technique is very beneficial to reactive deposition of transition-metal nitrides such as NbN coatings.

Investigating ion recombination effects in a liquid-filled ionization chamber array used for IMRT QA measurements.

PTW's Octavius 1000 SRS array performs IMRT quality assurance (QA) measurements with liquid-filled ionization chambers (LICs) to allow closer detector spacing and higher resolution, compared to air-filled QA devices. However, reduced ion mobility in LICs relative to air leads to increased ion recombination effects and reduced collection efficiencies that are dependent on Linac pulse frequency and pulse dose. These pulse parameters are variable during an IMRT delivery, which affects QA results. In this study, (1) 1000 SRS collection efficiencies were measured as a function of pulse frequency and pulse dose, (2) two methods were developed to correct changes in collection efficiencies during IMRT QA measurements, and the effects of these corrections on QA pass rates were compared. To obtain collection efficiencies, the OCTAVIUS 1000 SRS was used to measure open fields of varying pulse frequency, pulse dose, and beam energy with results normalized to air-filled chamber measurements. Changes in ratios of 1000 SRS to chamber measured dose were attributed to changing collection efficiencies, which were then correlated to pulse parameters using regression analysis. The usefulness of the derived corrections was then evaluated using 6 MV and 10FFF SBRT RapidArc plans delivered to the OCTAVIUS 4D system using a TrueBeam (Varian Medical Systems) linear accelerator equipped with a high definition multileaf collimator. For the first correction, matlab software was developed that calculates pulse frequency and pulse dose for each detector, using measurement and DICOM RT Plan files. Pulse information is converted to collection efficiency, and measurements are corrected by multiplying detector dose by ratios of calibration to measured collection efficiencies. For the second correction the MU/min in the daily 1000 SRS calibration was chosen to match the average MU/min of the volumetric modulated arc therapy plan. Effects of the two corrections on QA results were examined by performing 3D gamma analysis comparing predicted to measured dose, with and without corrections. Collection efficiencies correlated linearly to pulse dose, while correlations with pulse frequency were less defined, generally increasing as pulse frequency decreased. After complex matlab corrections, average 3D gamma pass rates improved by [0.07%,0.40%,1.17%] for 6 MV and [0.29%,1.40%,4.57%] for 10FFF using [3%/3 mm,2%/2 mm,1%/1 mm] criteria. Maximum changes in gamma pass rates were [0.43%,1.63%,3.05%] for 6 MV and [1.00%,4.80%,11.2%] for 10FFF using [3%/3 mm,2%/2 mm,1%/1 mm] criteria. On average, pass rates of simple daily calibration corrections were within 1% of complex matlab corrections. OCTAVIUS 1000 SRS ion recombination effects have little effect on 6 MV measurements. However, the effect could potentially be clinically significant for higher pulse dose unflattened beams when using tighter gamma tolerances, especially when small aperture sizes are used, as is common for SRS/SBRT. In addition, ion recombination effects are strongly correlated to changing MU/min, therefore MU/min used in daily 1000 SRS calibrations should be matched to the expected average MU/min of the IMRT plan.

Hardness and surface roughness of hydrogenated amorphous carbon films synthesized by atmospheric pressure plasma enhanced CVD method with various pulse frequencies

Atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD) has attracted much attention for its cost-effectiveness owing to eliminate the use of vacuum devices. We synthesized hydrogenated amorphous carbon (a-C:H) films under atmospheric pressure from C2H2 gas diluted with N2 with varying pulse frequency of plasma source. We investigated the effect of surface texture and chemical bonding structure of the films on hardness. The hardness, surface roughness and chemical content ratio were analyzed by tribo scope nano-mechanical indentation tester, atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS), respectively. As the pulse frequency decreased from 10 to 2kHz, the hardness increased from 0.35 to 0.92GPa and the surface roughness decreased from 49.8 to 14.3nm. From the result of XPS analysis, the N/C molar ratio increased from 0.022 to 0.094 with increasing the pulse frequency.

Control of ZCS-SR Inverter-Fed Voltage Multiplier-Based High-Voltage DC–DC Converter by Digitally Tuning Tank Capacitance and Slightly Varying Pulse Frequency

Conventional pulse-frequency-modulated (PFM) zero-current switching series resonant (SR) inverter-fed voltage-multiplier-based high-voltage dc power supplies have nearly zero switching loss. However, they have limitations of poor controllability at light load and large output voltage ripple at low switching frequencies. To address these problems, this letter proposes a new control scheme that is based on digitally tuning tank capacitance and slightly varying pulse frequency of SR inverter. For the realization of the proposed control approach, the tank circuit of the resonant inverter is made up of several tank capacitors that are switched into or out of the tank circuit by electromechanical switches. By digitally modulating the tank capacitance, the output voltage changes in steps. The regulation of output voltage between two adjacent steps is achieved by slightly varying the pulse frequency. The proposed control scheme has several features, namely, a wide range of output voltage controllability even at light loads, less output voltage ripple, and less current stress on the inverter's power switches at light loads. Therefore, the proposed control approach alleviates most of the problems associated with conventional PFM. Experimental results obtained from a scaled-down laboratory prototype are presented to verify the effectiveness of the proposed system.

Non-contact thrust stand calibration method for repetitively pulsed electric thrusters

A thrust stand calibration technique for use in testing repetitively pulsed electric thrusters for in-space propulsion has been developed and tested using a modified hanging pendulum thrust stand. In the implementation of this technique, current pulses are applied to a solenoid to produce a pulsed magnetic field that acts against a permanent magnet mounted to the thrust stand pendulum arm. The force on the magnet is applied in this non-contact manner, with the entire pulsed force transferred to the pendulum arm through a piezoelectric force transducer to provide a time-accurate force measurement. Modeling of the pendulum arm dynamics reveals that after an initial transient in thrust stand motion the quasi-steady average deflection of the thrust stand arm away from the unforced or "zero" position can be related to the average applied force through a simple linear Hooke's law relationship. Modeling demonstrates that this technique is universally applicable except when the pulsing period is increased to the point where it approaches the period of natural thrust stand motion. Calibration data were obtained using a modified hanging pendulum thrust stand previously used for steady-state thrust measurements. Data were obtained for varying impulse bit at constant pulse frequency and for varying pulse frequency. The two data sets exhibit excellent quantitative agreement with each other. The overall error on the linear regression fit used to determine the calibration coefficient was roughly 1%.

Super-resolution variable-dose imaging in digital radiography: quality and dose reduction with a fluoroscopic flat-panel detector

Super-resolution (SR) image processing produces a high-resolution image from a series of low-resolution images. The aim of this study was to evaluate SR-images based on fluoroscopic flat-detector (FD) acquisition at different frame rates. Fluoroscopic FD-sequences with 20 frames were obtained with varying pulse frequencies of (1) a line pair resolution phantom; (2) a low-contrast resolution phantom, and (3) a human knee specimen. Super-resolution digital radiographs (SR-Radiographs) were generated from each sequence. Variable-dose images were simulated by constructing SR-Radiographs using 6 and 12 frames from the corresponding fluoroscopic sequence. "Single Shot" and Computed Radiography (CR) images were obtained for comparison based on dynamic range and sharpness of bone detail structures. Patient-derived SR-Radiographic images were constructed to demonstrate clinical examples. The spatial resolution of SR-radiographs obtained at 12.5 frames per second (fps) and 6 fps were comparable with CR and "Single Shot" images, providing ~3.5 line pairs per mm (l p/mm). Similarly, low-contrast resolution of SR-radiographs obtained at 12.5, 6, and 30 fps were equivalent to CR and "Single Shot" images. The human knee specimen SR-radiograph obtained using 12 FD images at 12.5 fps was superior to a CR image in overall image quality, with a dose reduction of 75%. Variable-dose SR-radiographic simulations suggest a dose saving potential of 90-95% when using 6 FD images at 12.5 fps or 6 fps, respectively. The phantom testing images and simulation results demonstrate that diagnostic quality SR-radiographic images of skeletal extremities can be synthesized using a flat-panel detector system designed primarily for angiography. SR-images obtained with substantially reduced radiation dose are feasible, and this technology may improve digital radiography for pediatric, neonatal radiography, or mammography applications. Further testing is needed to validate super-resolution techniques in other body regions and for different flat-detector systems.

A thermal model for laser interaction with thick dielectric film on metallic substrate: Application to Ca–P layer on Ti alloy

Ca–P coatings on Ti–6Al–4V substrates were synthesized using a direct pulsed Nd:YAG laser writing technique. The phase and morphological evolutions within the coatings as a function of laser processing parameters were evaluated using X-ray diffraction and scanning electron microscopy techniques. A three dimensional modeling based on COMSOL's™ Multiphysics was adopted to understand the temperature evolution and corresponding cooling rate as a function of laser processing parameters. The temperature evolutions and cooling rate estimated from the model, satisfactorily explained the variation in phases and melt depth with varying pulse frequency of the laser beam.

Impact of varying pulse frequency and duration on muscle torque production and fatigue

Neuromuscular electrical stimulation (NMES) involves the use of electrical current to facilitate contraction of skeletal muscle. However, little is known concerning the effects of varying stimulation parameters on muscle function in humans. The purpose of this study was to determine the extent to which varying pulse duration and frequency altered torque production and fatigability of human skeletal muscle in vivo. Ten subjects underwent NMES-elicited contractions of varying pulse frequencies and durations as well as fatigue tests using stimulation trains of equal total charge, yet differing parametric settings at a constant voltage. Total charge was a strong predictor of torque production, and pulse trains with equal total charge elicited identical torque output. Despite similar torque output, higher- frequency trains caused greater fatigue. These data demonstrate the ability to predictably control torque output by simultaneously controlling pulse frequency and duration and suggest the need to minimize stimulation frequency to control fatigue.

Effect of Pulsed Plasma Processing on Controlling Nanostructure And Properties of Thin Film/Coatings

The benefits of pulsed plasma processing, including pulsing both cathode and substrate in physical vapour deposition (PVD) processes (magnetron sputtering and cathodic arc evaporation (CAE)) and the pulsed plasma enhanced chemical vapour deposition (P-PECVD) process were demonstrated by correlating the pulsed plasma process parameters, microstructure and properties. Five coating systems were developed for structural, electronic, functional and tribological applications. These are: pulsed reactive magnetron sputtering of TiO thin films; alumina deposition with pulsed plasma in closed field unbalanced magnetron sputtering; deposition of thin film silicon using P-PECVD; high energy pulsed bias assisted CAE of Cr–N graded coatings on 7075-T6 Al substrates; and sputter deposition of nickel anode on protonic BaCe0.9Y0.1O3–a electrolyte under pulsed dc biasing of substrate. Pulsed plasma was found to change particle energies and plasma composition in both PVD and CVD processes. Through controlled ion bombardment (ion energies and relative abundances of plasma species) by varying pulse frequency, pulse duration and bias voltage, film growth and therefore film properties can be tailored. The films became denser and nanostructured. The interface structure was graded, allowing superior adhesion. Better film performance (e.g. wear resistance, fracture toughness and efficiencies of solar cells and fuel cells) was achieved because of the modified film microstructure and architecture. These results clearly indicate the significant effects of the plasma species and their energies on modification of both the structure and properties of thin films. In several of these examples, the properties could not have been achieved in continuous dc magnetron sputtering. SE/518

Gaze shifts evoked by electrical stimulation of the superior colliculus in the head-unrestrained cat. I. Effect of the locus and of the parameters of stimulation.

Several studies have suggested that the pattern of neuronal activity in the superior colliculus (SC) interacts with the well-known topographical coding of saccades (motor map). To further describe this interaction, we recorded gaze saccades evoked by electrical microstimulation of SC deeper layers in the head-unrestrained cat and systematically varied the collicular locus (25 sites) and parameters (intensity, frequency) of the stimulation. Long stimulation trains were used to avoid saccade truncation. We found that the direction and amplitude of evoked gaze shifts were related to the stimulation locus, describing a gaze shift map. For 18 out of 20 sites the amplitude, but not the direction, also strongly depended on stimulation strength. Indeed, gaze amplitude continuously increased when raising current intensity up to several times the threshold value T (the largest intensity tested was 6 x T), whereas varying pulse frequency from 150 to 750 pulses per second (p.p.s.) revealed an optimal frequency range (300 and 500 p.p.s.) eliciting the largest gaze shifts. Moreover, the intensity effect on amplitude increased in an orderly fashion with the rostro-caudal stimulation locus. Gaze shift amplitude was not related to the number of delivered stimulation pulses. Concerning movement initiation, increasing either intensity or frequency led to an exponential decrease in gaze latency until minimal values near 30 ms were reached, but the number of pulses delivered during the corresponding latency period remained constant within a 300-500 p.p.s. frequency range. These findings indicate that the pattern of collicular discharge evoked by electrical stimulation strongly interacts with the gaze shift map and provide evidence for a summation of collicular activities by downstream premotor neurons.

Differential Effects of Gonadotropin-Releasing Hormone (GnRH) Pulse Frequency on Gonadotropin Subunit and GnRH Receptor Messenger Ribonucleic Acid Levels in Vitro*

The hypothalamic hormone, GnRH, is released and transported to the anterior pituitary in a pulsatile manner, where it binds to specific high-affinity receptors and regulates gonadotropin biosynthesis and secretion. The frequency of GnRH pulses changes under various physiological conditions, and varying GnRH pulse frequencies have been shown to regulate differentially the secretion of LH and FSH and the expression of the gonadotropin alpha, LH beta, and FSH beta subunit genes in vivo. We demonstrate differential effects of varying GnRH pulse frequency in vitro in superfused primary monolayer cultures of rat pituitary cells. Cells were treated with 10 nM GnRH pulses for 24 h at a frequency of every 0.5, 1, 2, or 4 h. alpha, LH beta, and FSH beta messenger RNA (mRNA) levels were increased by GnRH at all pulse frequencies alpha and LH beta mRNA levels and LH secretion were stimulated to the greatest extent at a GnRH pulse frequency of every 30 min, whereas FSH beta mRNA levels and FSH secretion were stimulated maximally at a lower GnRH pulse frequency, every 2 h. GnRH receptor (GnRHR) mRNA levels also were increased by GnRH at all pulse frequencies and were stimulated maximally at a GnRH pulse frequency of every 30 min. Similar results were obtained when the dose of each pulse of GnRH was adjusted to maintain a constant total cumulative dose of GnRH over 24 h. These data show that gonadotropin subunit gene expression is regulated differentially by varying GnRH pulse frequencies in vitro, suggesting that the differential effects of varying GnRH pulse frequencies on gonadotropin subunit gene expression occur directly at the level of the pituitary. The pattern of regulation of GnRHR mRNA levels correlated with that of alpha and LH beta but was different from that of FSH beta. This suggests that alpha and LH beta mRNA levels are maximally stimulated when GnRHR levels are relatively high, whereas FSH beta mRNA levels are maximally stimulated at lower levels of GnRHR expression, and that the mechanism for differential regulation of the gonadotropins by varying pulse frequencies of GnRH may involve levels of GnRHR. Furthermore, these data suggest that the mechanisms whereby varying GnRH pulse frequencies stimulate alpha LH beta, and GnRHR gene expression are similar, whereas the stimulation of FSH beta mRNA levels may be different.

A mechanism for the differential regulation of gonadotropin subunit gene expression by gonadotropin-releasing hormone.

The hypothalamic hormone gonadotropin-releasing hormone (GnRH) is released in a pulsatile fashion, with its frequency varying throughout the reproductive cycle. Varying pulse frequencies and amplitudes differentially regulate the biosynthesis and secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) by pituitary gonadotropes. The mechanism by which this occurs remains a major question in reproductive physiology. Previous studies have been limited by lack of available cell lines that express the LH and FSH subunit genes and respond to GnRH. We have overcome this limitation by transfecting the rat pituitary GH3 cell line with rat GnRH receptor (GnRHR) cDNA driven by a heterologous promoter. These cells, when cotransfected with regulatory regions of the common alpha, LH beta, or FSH beta subunit gene fused to a luciferase reporter gene, respond to GnRH with an increase in luciferase activity. Using this model, we demonstrate that different cell surface densities of the GnRHR result in the differential regulation of LH and FSH subunit gene expression by GnRH. This suggests that the differential regulation of gonadotropin subunit gene expression by GnRH observed in vivo in rats may, in turn, be mediated by varying gonadotrope cell surface GnRHR concentrations. This provides a physiologic mechanism by which a single ligand can act through a single receptor to regulate differentially the production of two hormones in the same cell.

Transmembrane voltage of opossum esophageal smooth muscle and its response to electrical stimulation of intrinsic nerves

This study was designed to examine the transmembrane potential of esophageal circular smooth muscle both before and in response to electrical stimulation of the intrinsic neural plexus, and to determine if regional differences are present in these potentials. Transverse strips of the opossum esophagus were prepared from sites located 1,3,5, and 7 cm above the gastroesophageal junction and subjected to 1-s trains of square-wave pulses. The effects of varying pulse frequency, voltage, and duration were assessed by conventional microelectrode techniques. The latency of the electrical off response ranged from a mean value of 1.08 s at 5 Hz to 1.0 s at 16 Hz when measured in cells from strips 5 cm above the gastroesophageal junction. Associated with this increase in latency is both an increase in the mean amplitude of hyperpolarization and a fall in the rate of the ensuing depolarization. In contrast, an increase in pulse voltage or duration had no effect on electrical off response latency. Resting potential analyzed on a regional basis ranged from a mean of −52.8 mV to −43.5 mV in strips 7 cm and 1 cm above the gastroesophageal junction respectively. Electrical off response latencies also demonstrated regional differences ranging from 1.06 to 1.50 s in strips taken 7 cm and 3 cm above the gastroesophageal junction respectively. Associated with the prolonged latencies noted in the more aboral strips was a decrease in the average rates of both membrane hyperpolarization and ensuing depolarization. It can be concluded from these studies that (a) within a given region an increase in stimulus frequency increases the mean amplitude of hyperpolarization, decreases the rate of the ensuing depolarization, and prolongs the electrical off response latency; (b) mean resting potential of esophageal circular smooth muscle cell becomes gradually less negative in an oral to aboral direction; and (c) cells of the more aboral smooth muscle segments studied demonstrated a decrease in the average rates of both membrane hyperpolarization and ensuing depolarization, and a prolonged electrical off response latency.

A changed dose-response in Saccharomyces at dose-rates above 10 7 rad per sec.

SummaryThe dose-response of a haploid wild-type Saccharomyces and its mutants rs1 and rs2 to ionizing radiation of a dose-rate of 1·2 × 107 rads/sec and 1 pulse per second was compared with that of dose-rates of 1·6–9·8 × 109 rads/sec and varying pulse frequencies in hypoxic conditions.Lower dose-rate exposures produced exponential, higher dose-rate exposures concave survival curves. Budding cells did not influence the shape of the survival curves.At the 10 per cent survival level, all cells are 30 per cent less sensitive at the lower than at the higher dose-rates. At lower survival levels the situation reverses. The change in sensitivity may be due to a fast healing process at the lower dose-rates and radical–radical interactions at higher dose-rates.